Learn Spanish (Spain): Quiero ir a la escuela.

Quiero comes from the verb querer (to want). It is a stem-changing verb, which means the vowel in the middle of the word changes when you conjugate it. For the 'I' form, the e changes to ie, giving us quiero.

Where is the word for 'I' (yo) in this sentence?

Because the verb form quiero already means 'I want', the pronoun yo is optional. Spanish speakers usually drop it unless they want to add special emphasis.

Why didn't we conjugate ir (to go)?

When you have two verbs working together to make one idea, like 'want to go', only the first verb gets conjugated (quiero). The second verb stays in its original dictionary form, called the infinitive (ir).

Why is there a la before escuela when English just says 'to school'?

In English, we often drop 'the' for general places like school, work, or church. In Spanish, you almost always need the article. So, you must literally say 'I want to go to the school' (a la escuela).